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New submitter QuantumPion writes
"The Environmental Protection Agency released draft guidelines last month that could significantly relax radiation hazard standards in the case of a radiological event in the United States by using risk-based decisions. The goal is to have limits that make sense in an emergency that are different from the limits in day-to-day life. From the article: 'Currently, the only guidance are the extremely strict standards that apply for EPA Superfund sites and nuclear plant decommissioning, which are as low as 0.010–0.025 rem/year, far below the natural background levels in the U.S. of 0.300 rem/year, and even well below the average amount of radioactive materials that Americans eat each year. And these guidelines aren’t really different from the 1992 PAG, except in the area of long-term cleanup standards and, perhaps, standards for resettlement. What’s the big deal here? As radworkers, we’re allowed to get 5 rem/year. 2 rem/year doesn’t rate a second thought. ... No one has ever been harmed by 5 rem/year, so setting emergency levels at 2 rem/year is pretty mild and more than reasonable. ... Think of it this way. The situations covered by these new guidelines are similar to someone dying of thirst who has the chance to drink fresh water having 2,000 pCi per gallon of radium in it. While the safe drinking water levels are 20 pCi/gal for Ra, 2,000 pCi/gal is of no threat, especially if you’re going to die from imminent dehydration. Of course, a bag of potato chips has 3,500 picocuries, so go figure.'"

Potatoes contain gobs of potassium, which has a naturally occurring radioactive isotope (K40). Bananas have the same issue. Unlike C14, K40 is primordial, so everywhere you have potassium, you have essentially the same concentration of K40.

The fact that there is naturally occurring radioactivity does not mean it is safe to add more.

But it is a good indication that one can safely add more. As to the rest of your post, look at the error bars of such studies. I bet you'll see no actual evidence of increased mortality for small doses of radiation. Instead you'll see evidence consistent with a wide range of possibilities.

silly, the people with the higher incidence of cancer in the hiroshima study had exposures of a good fraction of a gray (100 rem), e.g. half a gray at 1500 meters distance. that's way out of the league of what we're talking about here.

No. An 80-kilogram person has about 14 or 15 kg of carbon atoms. This works out to trillions of carbon atoms per human cell. Therefore every cell has approximately one atom of C14, and the human body as a whole has almost a quadrillion C14 atoms.

Because "radioactive environment" actually has to be quantified before it's meaningful. You're sitting in a radioactive environment right now. This is what you and the vast majority of Americans who grew up with the X-Men don't understand. So you have to talk about exactly how much radiation you're sitting in.

So let's talk about it. Let's say you weigh 70kg. That means you are made of approximately 7.0 x 10^26 carbon atoms (among other things). Carbon 14, a naturally occurring unstable radioactive isotope of carbon, makes up about 1 in every trillion carbon atoms. That's 1 in 1 x 10^11. Which means there are somewhere around 7 x 10^15 carbon 14 atoms inside you right now. Carbon 14 has a half life of 5730 years, give or take 40 years. That means that several thousand atoms of carbon 14 undergo radioactive decay inside you every second. I'll spare you the math, since there are already too many scary numbers in this post. That means there are thousands of beta particles running around loose inside you, every second of the day. In short, you are radioactive.

And... so what. Those thousands of decay events per second add up to a millirem per year, so tiny it's not even measurable by a normal Geiger counter. You are unavoidably exposed to radiation simply by existing. And here's what matters to you: that radiation you expose yourself to by being made of carbon has no measurable affect on your lifespan, or anyone else's. Something else will kill you first, long before the radiation of yourself induces a cancer inside yourself. Most cancers are chemically induced, not radioactively induced.

Now, the kicker is that Carbon, unlike Cesium or Iodine or Strontium or Plutonium, forms part of your DNA. And we have enough Carbon and cells, that about a dozen or so cells will literally have their DNA exploded from within by Carbon 14 *in* the DNA changing to Nitrogen-14.

Go ahead, calculate the exact number if you wish. Keep in mind this time there are about 3,200,000,000 base pairs in every cell's DNA.;) Which makes a few hundred Carbon-14 per cell *in* the DNA. And since there are (as you say), 80,000,000,000 cells, they are going off like popcorn! And that's just DNA, never mind the much larger rest of the cell.

And then there are the muons that will slam you from above with 1TeV energy every second, light up path, ionizing you from the tip of your head down and out your toes. Thousands to millions of ionized molecules, every second, day or night. And every half a minute or so, one of these muons will stop in your body and blow up like a little bomb.

Incorrect. Sieverts are specifically designed to account for the differences between radiation types with regards to biological effects. 1 Sv has the same biological impact regardless of whether it was caused by alpha, beta or gamma radiation. If the radiation is given in Grays, then you need to apply correction factors depending on radiation type.

tldr: Don't eat, drink or breathe radioactive gunk. It's worse for you than it looks.

This advice is pretty much worthless, since no one is going to intentionally ingest radioactive gunk. So here is some useful advice:1. Buy a shaker of "no-salt" (KCl) or "lite-salt" (mixture of NaCl and KCl).2. Buy a bottle of water purification tablets (iodine).3. Buy a bottle of calcium supplements.You should do this now (or the next time you go shopping) because if you wait till after a radioactive event, they will be sold out. When there is a leak/detonation/whatever, you add these to your diet. The copious amounts of these elements will cause your body to expel the surplus in your urine, along with most of the radioactive isotopes of the same elements (or strontium in the case of calcium). This simple $10-$20 investment may save your life.

Cesium doesn't linger in mammals. Depending on the tissues it lodges in after inhalation or ingestion (bone, fat, muscle etc.) its biological halflife is between 70 and 120 days i.e. half the cesium taken in will be pissed away or excreted in that time, then half the residue over the next period and so on. It's the same with strontium and a number of other problem specimens in the radiochemical zoo although the half-life varies from element to element.

Iodine-131 is the major contamination problem from fission releases, it's preferentially concentrated in the thyroid and is very radioactive but because of that it goes away quite quickly, with a halflife of only 8 days or so and superdosing with iodine tablets will prevent uptake of I-131 to a large extent. Hospitals and therapeutic facilities that use I-131 to "burn out" thyroid cancers flush residues into the sewer systems leading to the occasional panic when I-131 is detected in miniscule amounts in rivers, lakes etc. downstream.

Yes, eating certain radioisotopes is dangerous. Some isotopes concentrate in areas of the body and emit radiation that is much more harmful when it is in the body (alpha radiation).

However, The chart is given in Sv. Sv takes into account that some radiation is more harmful than others. So, the biological effects from 1 mSv should be the same whether it came from an alpha emmiter or a beta emmiter.

Again, some radionuclides concentrate in parts of the body (others are eliminated quickly - see effective halflife which combines radiological halflife and biological halflife). So, how can we know how many mSv we might get from ingesting one isotope or another? You want to look at commited dose [wikipedia.org]. This is a calculation of how much dose (mSv) you recieve from ingesting some radioisotope. You then use that figure, in mSv, to compare against the chart on xkcd. What you might be interested in is ALI [nucleonica.net] (annual limit on intake). This will give you an amount of a radionuclide (measured in activity or mass) that, if ingested, will give you the highest allowable dose (measured in mSv).

So, you can compare the damage done by various radioisotopes done to you in various ways if you are comparing them in the right units, mSv. But you couldn't compare them just by giving the amount of substance (without considering what kind of radiation and what in the body was irradiated). But, those calculations can be done, and the answer is given in mSv or mrem. This is why the xkcd chart uses mSv for the units, so that a meaningful comparison can be made.